We study bifurcation measurement of a multilevel superconducting qubit using a nonlinear resonator biased in the straddling regime, where the resonator frequency sits between two qubit transition frequencies. We find that high-fidelity bifurcation measurements are possible because of the enhanced qubit-state-dependent pull of the resonator frequency, the behavior of qubit-induced nonlinearities, and the reduced Purcell decay rate of the qubit that can be realized in this regime. Numerical simulations find up to a threefold improvement in qubit readout fidelity when operating in, rather than outside of, the straddling regime. High-fidelity measurements can be obtained at much smaller qubit-resonator couplings than current typical experimental realizations, reducing spectral crowding and potentially simplifying the implementation of multiqubit devices.We study bifurcation measurement of a multilevel superconducting qubit using a nonlinear resonator biased in the straddling regime, where the resonator frequency sits between two qubit transition frequencies. We find that high-fidelity bifurcation measurements are possible because of the enhanced qubit-state-dependent pull of the resonator frequency, the behavior of qubit-induced nonlinearities, and the reduced Purcell decay rate of the qubit that can be realized in this regime. Numerical simulations find up to a threefold improvement in qubit readout fidelity when operating in, rather than outside of, the straddling regime. High-fidelity measurements can be obtained at much smaller qubit-resonator couplings than current typical experimental realizations, reducing spectral crowding and potentially simplifying the implementation of multiqubit devices.

arXiv:1206.1296Physical Review AAug 23, 201214 citations

Optimization of Experimental Setups and Readout for Superconducting Qubits

Taryn V. Stefanski

Feb 1, 20250 citations

Large dispersive shift of cavity resonance induced by a superconducting flux qubit in the straddling regime

K. Inomata, Tsuyoshi Yamamoto, P.-M. Billangeon +2 more

We demonstrate enhancement of the dispersive frequency shift in a coplanar waveguide resonator induced by a capacitively coupled superconducting flux qubit in the straddling regime. The magnitude of the observed shift, 80 MHz for the qubit-resonator detuning of 5 GHz, is quantitatively explained by the generalized Rabi model which takes into account the contribution of the qubit higher energy levels. By applying the enhanced dispersive shift to the qubit readout, we achieved $90%$ contrast of the Rabi oscillations, which is mainly limited by the energy relaxation of the qubit.We demonstrate enhancement of the dispersive frequency shift in a coplanar waveguide resonator induced by a capacitively coupled superconducting flux qubit in the straddling regime. The magnitude of the observed shift, 80 MHz for the qubit-resonator detuning of 5 GHz, is quantitatively explained by the generalized Rabi model which takes into account the contribution of the qubit higher energy levels. By applying the enhanced dispersive shift to the qubit readout, we achieved $90%$ contrast of the Rabi oscillations, which is mainly limited by the energy relaxation of the qubit.

arXiv:1207.6825Physical Review BOct 26, 201264 citations

Readout fidelity enhancement via transient response exclusion in superconducting qubits

Wei-En Lin, Yung‐Fu Chen

Physical Review AFeb 27, 20260 citations

90%

contrast of the Rabi oscillations, which is mainly limited by the energy relaxation of the qubit.